val index : Index.t -> Equality.equality -> Index.t
val remove_index : Index.t -> Equality.equality -> Index.t
val in_index : Index.t -> Equality.equality -> bool
val index : Index.t -> Equality.equality -> Index.t
val remove_index : Index.t -> Equality.equality -> Index.t
val in_index : Index.t -> Equality.equality -> bool